CSRM — MeasurementSpecification missing documentation

Need to add documentation of MeasurementSpecification.summary (paragraph 7.28) and fix MeasurementSpecification.id missing documentation.

The summary element is missing documentation.
The id incorrectly indicates that it is the id of a requirement, rather than a MeasurementSpecification.

Add documentation to summary and fix documentation in summary

Add/change documentation as follows to the model and to the specification:

MeasurementSpecification.summary
add documentation: The summary is a textual description of constraints, and measurement activities used to provide insight into the progress made in the definition and development of the technical solution, risks, and issues.

MeasurementSpecification.id
From: The unique id of the requirement.
to: The id of the MeasurementSpecification.